When an interior of a room is heated or cooled, or is ventilated, temperature (sensible heat) and humidity (latent heat) are exchanged (total heat exchange) between fresh air supplied to the interior (supply air) and air exhausted from the interior (exhaust air), via a heat-exchange membrane.
In total heat exchange, for example, a heat-exchange membrane element is used, which includes a heat-exchange membrane and a resin frame body for supporting the membrane (e.g., Patent Document 1). FIGS. 1(a) and 1(b) are schematic perspective views of a membrane element and a total heat exchanger using the membrane elements, both of which are introduced as a conventional technique in Patent Document 1. FIGS. 2(a), 2(b), and 2(c) are schematic perspective views of membrane elements and a total heat exchanger using the membrane elements, both of which are introduced as an inventive example in Patent Document 1.
In the example of FIG. 1, a heat-exchange membrane element 41 comprises a heat-exchange membrane 11 and a resin frame body 21, both of which are separately produced. The resin frame body 21 includes two or more rod-like spacers (ribs) 31 formed in parallel with one another, and portions (parallel portions) 25 of the frame body 21, which are parallel to the rod-like spacers, are also formed so as to have thicknesses similar to (or greater than) those of the rod-like spacers 31. A total heat exchanger 51 can be formed by alternately stacking the resin frame bodies 21 and the heat-exchange membranes 11 so that the directions of the parallel portions 25 (and the rod-like spacers 31) are alternately changed. In the total heat exchanger 51, the parallel portions 25 separate a supply air flow path and an exhaust air flow path from each other, so as to allow total heat exchange between supply air and exhaust air via the heat-exchange membrane 11.
Further, in the example of FIG. 2, a pair of first and second heat-exchange membrane elements 42a and 42b is used, and a total heat exchanger 52 is formed by alternately stacking these elements. More specifically, the first heat-exchange membrane element 42a comprises a heat-exchange membrane 11 and a resin frame body 22a integrally molded with the membrane. Further, on one side of the heat-exchange membrane 11, two or more rod-like spacers (ribs) 32a are formed in parallel with one another, and also on the other side of the heat-exchange membrane 11, two or more rod-like spacers (ribs) 33a are formed in parallel with one another. The spacers 32a on the one side are orthogonal to the spacers 33a on the other side. In addition, portions (parallel portions A) 26a of the frame body 22a, which are parallel to the rod-like spacers 32a on the one side, are formed so as to have thicknesses similar to (or greater than) those of the parallel rod-like spacers 32a. Further, portions (parallel portion B) 27a parallel to the rod-like spacers 33a on the other side are also formed so as to have thicknesses similar to (or greater than) those of the parallel rod-like spacers 33a. 
The second heat-exchange membrane element 42b has a structure similar to the first heat-exchange membrane element 42a. Further, in the spacers of the second heat-exchange membrane element 42b, second engaging portions 34b for positioning are formed. Accordingly, the second engaging portions 34b are engaged with first engaging portions 34a likewise formed in the first heat-exchange membrane element 42a, so as to prevent the positions of the elements 42a and 42b from deviating from each other. When the total heat exchanger 52 is formed, the first and second heat-exchange membrane elements 42a and 42b are alternately stacked so that the directions of the spacers (ribs) 32a and 32b, and 33a and 33b, which are opposed to one another, are aligned.
Also in the heat exchanger 52 of FIG. 2, the parallel portions 26a, 26b, 27a, and 27b separate a supply air flow path and an exhaust air flow path from each other, so as to allow total heat exchange between supply air and exhaust air via the heat exchange membrane 11.
An ordinary plastic film or metal foil allows the exchange of temperature (sensible heat), but does not allow the exchange of humidity (latent heat), and therefore, it cannot be used as a total heat exchange membrane. Thus, paper is used as a total heat exchange membrane in Patent Document 1, and a paper base material is disclosed also in Patent Document 2. A paper base material has the advantage of a high latent heat exchange rate, but has a low resistance to dew condensation. Thus, the total heat exchange membrane (paper) may be torn, if condensed dew is frozen.
Further, for example, as shown in Patent Document 3, a porous resin film such as an expanded porous polytetrafluoroethylene film is also used as a total heat exchange membrane. A porous resin film has an excellent resistance to dew condensation.